Biology and development of the sheep headfly Hydrotaea irritans (Fall.) (Diptera, Muscidae)

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Abstract
The biology and population fluctuations of the non-biting Muscid Hydrotaea irritans (Fall.) were studied in two contrasting areas of Surrey using a standardised catching technique at selected sites, by analysing catches and by dissecting the collected flies. Following the first appearance of adults in early June, catches reached a maximum in late July, the males having fallen to a small proportion by early July. During August catches gradually fell, remaining at a relatively low level for the rest of the summer. The complete life-cycle, starting with eggs from caged fly colonies, took 295 days under sheltered outdoor conditions. The fly is univoltine, with three larval instars; larvae leave the egg in the second instar which is a brief, saprophagous stage, while the third, principal stage is predatory on other insect larvae. Overwintering normally occurs as a late-stage larva. Flies collected from sheep-grazing areas in Northumberland were shown, using serological methods, to have fed predominantly on cattle blood protein.